1. Field of the Invention
This invention relates to an apparatus for supporting a substrate formed of a silicon wafer or the like to be exposed and, more particularly, to a substrate supporting unit detachably attached to an exposure apparatus and arranged to receive and deliver a wafer substrate or the like at a position remote from the exposure apparatus.
2. Description of the Related Art
Generally, in exposure apparatuses for manufacturing semiconductor devices, a substrate supporting unit detachable from the exposure apparatus is provided. The substrate supporting unit is used to receive and deliver a wafer substrate or the like (hereinafter referred to simply as "substrate") by being transported between positions on the inside and the outside of the exposure apparatus.
That is, as shown in FIG. 7, a substrate W extracted from a substrate storage rack R is transported to a rotating transport hand H to a delivery position on an attraction plate 51 of a substrate supporting unit A. After receiving the substrate W under the transport hand H, the substrate supporting unit A is operated to position the substrate W relative to the attraction plate 51 and is transported to an exposure apparatus S.
FIGS. 8 and 9 show an example of such a conventional substrate supporting unit. An attraction plate 51 which is a main body of the substrate supporting unit has attraction grooves 51a formed in its surface to attract a substrate W by a vacuum. The attraction grooves 51a communicate, through an internal piping 51b, with a pressure controller which includes a vacuum pump and a pressurized air supply source. Positioning for adjusting the position of the substrate W relative to the attraction plate 51 is performed by a first positioning means consisting of a pair of reference pins 66a and 66b fixed on the attraction plate 51 close to one of two opposite first sides of the same and a pressing pin 62 disposed close to the other of the two opposite first sides, and by a second positioning means consisting of a reference pin 72 fixed on the attraction plate 51 close to one of two opposite second sides perpendicular to the two opposite first sides and a pressing pin 69 disposed close to the other of the two opposite second sides.
For this positioning operation, a vacuum attraction force acting through the attraction grooves 51a is first removed and pressurized air is then supplied to make the substrate float on the attraction plate 51. Thereafter, operating pressures in cylinders 62b and 69b which have maintained the pressing pins 62 and 69 in a retracted state against the pressing resilience forces of springs 62a and 69a, respectively, are removed. The pressing pins 62 and 69 released from the operating pressures of the cylinders 62b and 69b, respectively, are moved in the directions of the arrows shown in FIG. 8 by the forces of the springs 62a and 69a until the substrate W is brought into abutment against the reference pins 66a, 66b, and 72.
After the substrate W has been positioned in this manner, the vacuum attraction force is supplied again to act through the attraction grooves 51a so that the substrate W is attracted to the attraction plate 51. While the substrate W is maintained in this state, the substrate supporting unit A is transported into the exposure apparatus S. In the exposure apparatus S, the substrate W is irradiated with radioactive rays such as g-rays, i-rays, excimer laser light, and X-rays to transfer a semiconductor circuit pattern on the substrate W to a semiconductor substrate, a liquid crystal panel, or the like. A semiconductor device, a liquid crystal panel or the like is thereby manufactured.
In the above-described conventional process, however, the upper surface of the attraction plate is finished so as to be specular, having the effect of correcting the flatness of the substrate, and the substrate to be attracted is a thin plate having two surfaces also finished so as to be specular. For this reason, when the vacuum attraction force through the attraction grooves is removed and, conversely, pressure size air is jetted to float the substrate on the attraction plate after the substrate has been received from the transport hand, a phenomenon of local linking (adhesion) between the surfaces of the attraction plate and the substrate made specular as described above can occur easily, whereby the substrate is deformed so that the substrate cannot suitably float. In such a situation, positioning of the substrate on the attraction plate using the pressing pins cannot be performed smoothly, and there is a risk of the substrate and the reference pins being damaged by a collision therebetween and there is a risk of abrasion of the surface of the attraction plate. Also, the amount of dust thereby caused to land on the substrate may be so large that a transfer defocus occurs.
If an impurity is mixed in the pressurized air for floating the substrate, there is a risk of the substrate being contaminated. Further, since the substrate is pressed against each reference pin in a horizontal direction as shown in FIG. 9, the pressing resilience force of each pressing pin may impede the vacuum attraction of the substrate to the attraction plate after the positioning operation, if it is excessively large relative to the force of the vacuum attraction force of the attraction plate. Conversely, if the resilience force is excessively small, the pressing force of the pressing pin may be insufficient to maintain the desired positioning accuracy. Thus, a high degree of accuracy is required in adjusting the pressing resilience forces of the springs.